Greenback Cutthroat Trout in the Colorado River Basin: The original homestead?

Authors: R. Paul Evans, Dennis K. Shiozawa, Peter J. Unmack, Jason Mathis

Year: 2010 (xlii)

Abstract

Cutthroat trout, Oncorhynchus clarkii, comprise at least 14 subspecies in western North America. The subspecies are typically found in geographically isolated drainages. Efforts to restore some of the most seriously threatened or endangered Cutthroat trout subspecies are required as the result of introgression, predation, and competition from introduced trouts as well as general habitat degradation. These impacts have clouded the original distribution and origins of the multiple subspecies. We present data and analyses based on sequence of half the mitochondrial genome covering multiple genes. Three main groupings were found. One group formed a basal cluster consisting of O. c. clarkii, Coastal Cutthroat Trout, O. c. henshawi, Lahontan Cutthroat Trout, and O. c. lewisi, Westslope Cutthroat Trout. The remaining two groups are sister lineages. One consists of O. c. bouvieri, Yellowstone Cutthroat Trout and O. c. utah, of the Bear River Basin of Utah and Idaho (Bear River Bonneville Cutthroat Trout). The other lineage consists of O. c. pleuriticus, Colorado River Cutthroat Trout, O. c. stomias, Greenback Cutthroat Trout, O. c. virginalis, Rio Grande Cutthroat Trout and O. c. utah, Bonneville Cutthroat Trout. We found moderate to strong resolution between the three lineages, but mostly poor resolution within each lineage. To clarify the biogeographical history of Greenback cutthroat trout, the mtDNA sequences of multiple genes were also analysed for Greenback Cutthroat trout populations from the east and west side of the Continental Divide. The greatest amount of sequence diversity was discovered in the Colorado River Basin populations as compared to the Arkansas or South Platte populations. These data suggest that Greenback Cutthroat trout recognized on the east side of the Continental Divide originated in the Colorado River basin and that the Greenback Cutthroat populations in the Colorado River basin are native. Colorado River Cutthroat trout were further examined to help resolve their possible origin in the northern Colorado River basin.